The present invention relates to an oscillator and more particularly to an oscillator of the type that includes two directly cross-coupled inverters each of which comprises a transistor connected between a first and second resistor and with a frequency-determining element connected in parallel with one of the resistors in one of the inverters.
From DE-OS No. 31 04 849, which corresponds to U.S. Pat. No. 4,518,933 (5/21/85), a quartz oscillator is known which comprises one connection pin for a quartz crystal, two transistor pairs, and a transistor which is connected as an emitter follower and which serves for connection to a power supply voltage. The emitter-connected transistor is preceded by a bias voltage generator with a diode series connection or the like. The collectors of one transistor pair are connected, via a respective collector impedance, to the emitter of the transistor which serves for the supply of power and also to a respective base of a transistor of the other transistor pair whose collectors are also connected to the emitter of the aforesaid power supply transistor. The oscillator voltage can be coupled out between the emitters of this transistor pair. These emitters are also connected to a respective base of a transistor of the former transistor pair, each of the emitters of which has an emitter impedance connected to the negative pole of the power supply voltage. A capacitor is connected parallel to one emitter impedance and a series connection of a quartz crystal and a capacitor is connected parallel to the other emitter impedance. Even tough the integrated circuit version of this oscillator requires only one connection pin for the quartz crystal, the circuit, inter alia, is very intricate and not suitable for driving an external load without using an additional output driver stage. It also requires a large chip surface area because of the large number of components and exhibits, as tests have shown, comparatively large frequency variations in dependence on the power supply voltage.